1. Field of the Invention
The present invention relates generally to an industrial gas turbine engine, and more specifically to a method for detecting a crack or other defect on a turbine rotor blade during operation of the engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as an industrial gas turbine engine, includes a turbine section with one or more stages or rows of turbine rotator blades that are exposed to a hot gas stream passing through the turbine. In order to allow for high turbine inlet temperatures, the turbine airfoils—which include stator vanes and rotor blades—are cooled by passing cooling air through the airfoils to limit a metal temperature. The turbine airfoils also include a TBC or thermal barrier coating to provide additional protection to the airfoil surfaces from the hot gas stream.
For an industrial gas turbine engine, part life is a main design concern due to the fact that an industrial engine must be capable of operating for very long periods of time without shutting down the engine as opposed to an aero engine which operates only during flight. A part such as a turbine rotor blade is exposed to high temperatures that will cause erosion or other damage if the part is not properly protected from the high temperature exposure. Turbine blades rotate at around 3,600 rpm and thus are under high stress loading. In a turbine rotor blade, the airfoil leading and trailing edges and the transition between the airfoil and a platform are areas that are under high thermal loads and thus a high probability of stress loads. These sections of the blade are the most likely locations for crack development.
Turbine airfoils like rotor blades are also subject to damage such as holes being formed or spallation of the TBC which will subject the external airfoil surface to direct exposure to the hot gas stream.
Several references are known in which an IR or infra-red camera is used to monitor a condition of a turbine rotor blade while in operation in the engine. U.S. Pat. No. 7,298,818 issued to Subramaniam et al. on Nov. 20, 2007 entitled METHOFOLOGIES FOR NON-DESTRUCTIVE QUANTIFICATION OF THERMAL BARRIER COATING TEMPERATURE ON SERVICE RUN PARTS discloses Methodologies for non-destructively inspecting and characterizing micro-structural features in a thermal barrier coating (TBC) on a component, wherein the micro-structural features define pores and cracks, if any, in the TBC. The micro-structural features having characteristics at least in part based on a type of process used for developing the TBC and affected by operational thermal loads to which a TBC is exposed. In one embodiment, the method allows detecting micro-structural features in a TBC, wherein the detecting of the micro-structural features is based on energy transmitted through the TBC, such as may be performed with a micro-feature detection system. The transmitted energy is processed to generate data representative of the micro-structural features, such as may be generated by a controller. The data representative of the micro-structural features is processed (e.g., by a processor) to determine at least one of the following: volumetric porosity information for the TBC and variation in the characteristics of the micro-structural features over a thickness of the TBC. Based on the results of the data processing, information is generated regarding at least one of the following: a present condition of the thermal barrier coating and a future likely condition of the thermal barrier coating. In another embodiment, one can estimate a level of thermal load to which the thermal barrier coating has been exposed.
U.S. Pat. No. 7,376,518 issued to Subramanian et al. on May 20, 2008 and entitled SYSTEM AND COMPUTER PROGRAM PRODUCT FOR NON-DESTRUCTIVE QUANTIFICATION OF THERMAL BARRIER COATING TEMPERATURES ON SERVICE RUN PARTS discloses a System and computer program product for non-destructively inspecting and characterizing micro-structural features in a thermal barrier coating (TBC) on a component, wherein the micro-structural features define pores and cracks, if any, in the TBC. The micro-structural features having characteristics at least in part based on a type of process used for developing the TBC and affected by operational thermal loads to which a TBC is exposed. In one embodiment, the method allows detecting micro-structural features in a TBC, wherein the detecting of the micro-structural features is based on energy transmitted through the TBC, such as may be performed with a micro-feature detection system 20. The transmitted energy is processed to generate data representative of the micro-structural features, such as may be generated by a controller 26. The data representative of the micro-structural features is processed (e.g., by a processor 30) to determine at least one of the following: volumetric porosity information for the TBC and variation in the characteristics of the micro-structural features over a thickness of the TBC. Based on the results of the data processing, information is generated regarding at least one of the following: a present condition of the thermal barrier coating and a future likely condition of the thermal barrier coating. In another embodiment, one can estimate a level of thermal load to which the thermal barrier coating has been exposed.
U.S. Pat. No. 7,432,505 issued to Brummel on Oct. 7, 2008 and entitled INFRARED-BASED METHOD discloses an online method, system, and computer-readable code for remotely monitoring radiant energy emitted from a turbine blade, which may be undergoing an incipient degradation, such as a crack, in a relatively low-temperature, and saturated steam environment of the low pressure stage of a steam turbine. The method and system provide sufficient temporal and spatial resolution to obtain high quality infrared images of the blade areas of interest enabling the system to identify the crack at any of those areas of the blade prior to such a crack growing to a critical length.
U.S. Pat. No. 8,063,372 issued to Lemieux et al. on Nov. 22, 2011 and entitled APPARATUS AND METHOD FOR TEMPERATURE MAPPING A ROTATING TURBINE COMPONENT IN A HIGH TEMPERATURE COMBUSTION ENVIRONMENT discloses an apparatus and method for temperature mapping a rotating component in a high temperature combustion environment. The apparatus includes a thermal imager having a field of view to sense infrared (IR) emissions. Emissivity of a surface of the component is subject to variation in the combustion environment. A radiance emitter defines a spot within the field of view of the thermal imager. The spot indicates a respective emissivity value. A processor is connected to the thermal imager to generate a radiance map of the component based on the IR emissions from the component. The processor includes a thermal calibration module configured to calibrate the radiance map based on the emissivity value of the spot within the field of view of the thermal imager to generate a calibrated thermal map of the component that displays absolute temperature over the surface of the component.